In order to utilize the engine of a truck to provide power for load handling equipment it is necessary to fit a power take-off unit, often referred to as a PTO. Power from this unit can be transferred either mechanically via a propeller shaft or belts, or hydraulically by fitting a hydraulic pump to the power take-off. These PTOs include shifters to operate the PTOs which are actuated by air, hydraulic fluid, or mechanical cables.
In some newer vehicles, there is no room for direct attachment of the PTO as other components are positioned where the PTO would be mounted. On one vehicle, the 4WD transfer case interferes with the positioning of the PTO on the transmission. In such cases, a split shaft can be attached to an output of the transmission and a PTO attached to the split shaft. The split shaft is typically engaged and disengaged using pressurized air. However, in vehicles having automatic transmissions, a source of air is typically not available. These air shift split shaft systems then require an add-on, small compressor and tank to supply the system.
The automatic transmission does have a readily available source of pressurized hydraulic fluid. However, the shifter assembly of the split shaft has never operated hydraulically. In addition, the pistons in the power take off units have a bleed hole in the piston of the shifter that helps speed up the release of the clutch. This results in the dumping of hydraulic fluid into the PTO which if the PTO is attached to the transmission, is not a problem. If the PTO is attached to a split shaft, then the hydraulic fluid dumps into the split shaft which is not fluidly connected to the transmission. Eventually the transmission would be starved of fluid and the split shaft would fill and overflow. In order to use the prior art power take off hydraulic shift system, there needs to be a way to get the fluid from the split shift back to the transmission. Attaching a gravity feed from the split shaft to the transmission would not overcome the problem as the flow back to the transmission would be too slow.